Double Clutching (the easy way)

In another thread, several people expressed a desire to learn how to double
clutch. I found this article which gives a good account on how to do it
properly. The main thing to remember is you car is always talking to you,
so learn to listen. You need to learn what rpm generates what speed in
each gear. Tach's are great for this, but engine sound is a much better
method. You don't always have time look at the tack. This procedure needs
to be done quickly and SMOOTHLY. So turn off the boom-box and go have some
fun.

I was afraid to post the link, so this is a C&P. I have included the
authors name for credit.

John

The following is a beginner's approach to learning how to double - clutch.
This technique allows downshifts from higher speeds without any
synchroniser wear. This is VERY important if you ever want to drive really
quickly and keep your transmission intact for extended periods!

The Easy Way to Double-Clutch
By Jeff Krause.

Double-clutching is the proper way to downshift at speed without placing
excessive wear on the transmission's synchronizers. This allows you to
select a much lower gear without the tell-tale lurch you normally get when
the clutch is let out after downshifting.

When downshifting my BMW M5 from 4th gear to 2nd at 50 mph, I need to raise
the engine speed from 2200 rpm to 5000. To prevent excessive synchroniser
wear, the clutch is depressed and the shifter is moved to neutral. The
clutch is then released, and the gas is depressed to bring the engine speed
up to where it needs to be for the lower gear. The clutch is then depressed
again and the shift lever moved into the lower gear. When the clutch is
released the second time, the engine is already turning the proper speed .
While this sounds complicated, it's easier done than said, and only takes
about a second.

To better understand how the process works, a little background on
transmission fundamentals will help.

A typical transmisson has two shafts, one connected to the engine through
the clutch, and one connected to the rear wheels. There are usually four to
six sets of gears on these shafts and they are selected with the gearshift
lever inside the car. When changing gears, the clutch is depressed to
disconnect the engine from the transmission so there isn't any stress on
the moving parts. Since the output shaft is permanently connected to the
rear wheels, the only way to match the speed of the two shafts is to use
the throttle to adjust engine speed.

Once the engine is turning the right rpm, both shafts will be turning the
same speed, and the gear lever will fall into gear WITHOUT using the
clutch! (Although most of the time you are shifting too fast to be that
accurate)

EXCERCISES

1) With the car idling in neutral, slowly step on the gas until the engine
is turning 3500 rpm. Do it again bringing the rpm's up more and more
quickly until you can give the pedal a quick stab and have the revs stop
where you want . As you shorten the time allowed to match revs, you will
notice it takes more throttle. In fast driving, you will be shifting so
fast 4 will take full thottle! Now try matching revs at 4000 rpm.

2) Find a deserted road, and maintain 40 mph in 4th gear. Now shift into
3rd, and see how many rpm's the engine speed increased. At this speed, the
difference won't be very much - maybe only a few hundred rpm. Go back into
4th gear. This time put the clutch in, push the lever to neutral and let
the clutch back out. You are now coasting with the clutch out. Raise the
engine speed to where it will be in third gear. Quickly push the clutch in,
select 3rd gear, and let the clutch out. There should be no perceptible
lurch if you accurately matched revs. Try the same thing at higher and
higher speeds. As the road speed goes up, the speed difference between
gears will go up as well. When going from 5th to 3rd a highway speeds, you
may end up within 1000 rpm of redline. The easiest way of determining your
maximum downshift speed is to watch the tach and speedo as you are shifting
up at redline. If you shift at redline from 2nd to 3rd at 60 mph, subtract
10 mph, and that becomes your effective maximum downshift point for 2nd
gear. If are within 10 mph, you are better off staying in the higher
gear.

HEEL-AND-TOE DOWNSHIFTS

This combines double-clutching and braking into one event. Place your foot
on the brake as far to the right as you comfortably can. While braking,
roll your ankle so you can catch the left edge of the gas pedal with the
right edge of your foot. If the pedals are too wide, try placing the ball
of your foot on the brake, and the heel on the gas (This is where the term
heel-and-toe originally came from). Now try gently slowing down and
downshifting. With practice, you can brake hard and downshift in one smooth
motion. This will prevent the wheels from locking when the clutch is let
out in the lower gear, and you will be ready for a burst of acceleration
coming out of your favorite corner!

Copyright The Driver's Edge 1997

jcutsh

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